The present invention relates to a cement-bound material.
Various examples show that the durability of reinforced concrete structures is substantially lower than was assumed during their planning. For this reason up to half the national expenditure in the field of construction goes in industrial countries towards the repair of existing buildings. Even such repair measures often do not show the desired durability. This is due to the fact that efficient materials and material systems are still missing which give the desired durability both to new buildings as well as the repair of existing buildings.
The occurring damage is mainly based on the following mechanisms:
1. Cement-bound materials are brittle and are subjected to differential shrinkage deformations after their production. These two phenomena lead to a complex inherent tension state and to the formation of cracks on the surface of the building component. These cracks facilitate the access of substances which lead both to the destruction of the concrete (sulfate) as well as to corrosion of the armoring (chlorides from anti-freeze salts). The corrosion products comprise a volume which is up to three times larger, leading to the chipping off of the concrete and to the exposure of the steel armoring.
2. Cement-bound materials are porous systems which absorb damaging substances (sulfates, chlorides, acids) into the pore system at their surface by capillary suction, diffusion and permeation.
3. Conventional cement-bound materials (primarily concrete) need to be compacted after their introduction into a shuttering by means of vibration machines in order to achieve a homogeneous structure. This work process is often not performed with the required diligence, leading to the consequence that the concrete is inhomogeneous and the absorption of damaging substances is strongly increased locally.
There are measures and products that are capable of preventing or ameliorating certain of the above damage mechanisms. For example, it is known from EP-A-0 286 112 to add synthetic fibers as a reinforcement for cement mortar or concrete, which fibers consist of monofilaments with a tensile strength of a maximum of 80 kg/mm2. From U.S. Pat. No. 4,261,754 a reinforcing fiber element is known which consists of oriented polyolefins in order to reinforce a matrix material such as cement. The fibers have a varying cross section in the longitudinal direction and roughened surfaces from which fibrils project. In U.S. Pat. No. 4,483,727 a method for producing bundles made of polyethylene fibers is described which is used for reinforcing brittle material such as cement, concrete plaster of Paris or the like. From U.S. Pat. No. 4,968,561 a synthetic monofilament made of polyvinyl alcohol is known which is used as a reinforcement for cement mortar or concrete. U.S. Pat. No. 5,399,195 describes a method for producing a cement material which reduces self-induced cracking. For this purpose synthetic fiber bundles are added, which bundles consist of 10 to 10,000 filaments per bundle. The filaments substantially consist of polyolefins, polyolefin derivatives and a polyester. Moreover, so-called corrosion inhibitors are known from U.S. Pat. No. 6,071,436 and U.S. Pat. No. 6,174,461. So-called waterproofing agents are known from U.S. Pat. Nos. 5,531,812 and 6,139,622 which make the surfaces of the concrete water-repellent. For this purpose aqueous solutions made of alkoxyl silanes, organic silanes and organic siloxane resins are used.
There are no efficient concepts for material systems which are capable of preventing all damaging mechanisms and their causes to such an extent that the durability can be increased several times over as compared with currently used methods.
The present invention is now based on the object of providing a cement-bound material which shows a considerably higher durability and is especially suitable for repairing existing buildings.
This object is achieved by a cement-bound material having a mineral binding agent, the cement-bound material comprising a mass hydrophobing agent selected from the group consisting of stearates, siliconates, silanes and siloxanes ranging from 0.5 to 20 wt. % with regard to the weight of the mineral binding agent, and a corrosion inhibitor which is capable of migrating and which is selected from the group consisting of nitrites, benzoates, amino alcohols and sodium monofluorophospahtes ranging from 0.1 to 20 kg per m3 of the material. In another embodiment, a cement-bound material having a mineral binding agent is provided, wherein the cement-bound material comprises a mass hydrophobing agent selected from the group consisting of stearates, siliconates, silanes and siloxanes ranging from 0.5 to 20 wt. % with regard to the weight of the mineral binding agent, and flexible fibers with a height-width ratio of 10 to 1000, preferably 200 to 600, a tensile strength of 0.8 to 4.0 GPa and a modulus of elasticity of 20 to 230 GPa, preferably higher than 25 GPa, wherein the fibers are present in an amount of 0.1 to 4.0% preferably 0.5 to 3.0%, by total volume.
The material in accordance with the invention comes with the major advantage that as a result of mass hydrophobing the penetration of contaminant-containing water is prevented and thus the durability of repairs is increased considerably. The armoring steel is retroactively protected against corrosion by adding migration-capable corrosion inhibitors.